1. Extracellular UTP and ATP show obvious similarities in their control of several metabolic functions of rat isolated hepatocytes. 2. They have a similar time-course and concentration-dependency for the activation of glycogen phosphorylase, the generation of inositol trisphosphate (IP3), the inhibition of glycogen synthase and the lowering of adenosine 3':5'-cyclic monophosphate (cyclic AMP) levels. 3. There is a similar synergism of the nucleotides with glucagon in activating phosphorylase. 4. They undergo a similar inhibition by phorbol myristic acid of their glycogenolytic effect. 5. The ATP and UTP effect on IP3 levels are not additive. 6. It is tentatively concluded that UTP and ATP use a common receptor.